Crude oil is a complex mixture of hydrocarbons and heteroatomic organic compounds of varying molecular weight and polarity. A common practice in the petroleum industry is to separate crude oil into four chemically distinct fractions: saturates, aromatics, asphaltenes, and resins.
Oil production from a well can decline suddenly or over time due to precipitation of solids, with one of the most serious precipitation problems being the creation of formation damage, i.e. partial or complete blockage by precipitated solids (asphaltenes, paraffins) within the formation in-flow production zone, on the well casing and even its associated equipment through which hydrocarbons and co-produced water must pass in order to be extracted from the well for recovery. Another problem is the adsorption of asphaltenes on the reservoirs mineral surfaces, whereby the wettability of the reservoir is changed from the preferred water-wet condition to a oil-wet condition and thereby further reducing the potential oil recovery. If the plugging damage of crude contaminants and deposited crude oil constituents on the well formations adjacent to the well casings and the well casings and its associated equipment is periodically removed, and the wettability of the reservoir returned to a more nascent-like water-wet and hydrophobic formation water condition, the overall production of the “treated” well can be expected to return to its previous or even improved productivity. In spite of treatment, over time, the crude oil production may gradually decrease as the precipitation and wettability problems slowly recurs or sudden decline may occur again requiring further treatment to restore its productivity.
Current techniques for removing these contaminants and solids via treating (could be viewed as cleaning) an oil well include the injection of various well-known solvents, oils, acids, bases, liquefied gases, water, alcohols, glycols, and glycol ethers and various mixtures of these liquids into the well where they are given time to work followed by removal. The injected treatment fluids generally cause the asphaltines and paraffins in the zone to break up and remix into the crude so they can be removed from the well. The various fluids also dissolve, disperse, or suspend a variety of other contaminants such as scale, drilling residues, rust and the like which may be also be obstructing the casing, perforations, or nearby formation to varying degrees, thereby allowing oil in the production zone to more readily flow into the casing and eventually be brought to the surface. Additionally, the treatment fluids may be used to break down and remove asphaltenes precipitated on the formations mineral surfaces and may assist in returning the well to a preferred water-wet condition.
The treatment fluids are injected into the well, under varying pressure and volume conditions, depending on the well conditions and treatment objectives, allowed to remain in the well for a period of time, which also varies according to the fluid and well conditions, then the mixture is drawn out of the well with the expectation that the mixture will remove most of the deposited contaminants that have collected on the well casings, perforations, and the porous formation adjacent the perforated well casings. One such treatment fluid includes the use of petroleum distillates (hot or cold). Another such treatment fluid mixture includes the use of hydrochloric and other acids. Yet another treatment fluid mixture includes aromatic solvents such as xylene, toluene etc. Other treatment fluid mixtures include one or more types of liquefied gases. Additionally, other treatment fluid mixtures might include any of the previously mentioned fluids with the addition of short chain alcohols, glycols and/or glycol ethers, or fresh or saline waters.
In order to effectively remove the built-up contaminants and precipitated solids on the well casings and the adjacent formations, the casings and formations must be effectively wet to enhance removal of the contaminants and crude oil. While the foregoing treatment fluids are effective to varying degrees, the cleaning effectiveness of these fluids would be increased by the addition of an additive that substantially improves the wetting properties of the treatment fluids or mixtures. What is needed is a well treatment fluid additive that increases cleaning effectiveness by improving the overall wetting properties of the treatment fluid. What is also needed is a well treatment fluid additive that provides substantially improved treatment effectiveness resulting in higher volume production and extension of the time interval these higher volumes occur before the well production declines and another treatment cycle is required.